Synergistic Effects of Mesoporous Structure and Oxygen Vacancies in SnO₂ for Enhanced CO₂ Electroreduction

Electrocatalytic CO₂ reduction (CO₂RR) into value-added chemicals represents a promising strategy for sustainable CO₂ utilization. This strategy relies on nanoscale structural engineering to gain desired CO₂RR catalyst performance, which is insufficiently understood. For example, how the pore structure, defect distribution, and surface reconstruction can be used to promote catalytic activity and material stability is not clarified. Here, we investigate how mesopores and oxygen vacancies (V_O) synergistically regulate the CO₂RR behavior of SnO₂. Mesoporous SnO₂ (M-SnO₂) synthesized hydrothermally shows enhanced mesoporosity and a higher specific surface area (59 vs. 21 m² g^-1) than bulk SnO₂ (B-SnO₂), achieving a Faradaic efficiency (FE) of 50.9% for formate at -1.15 V vs. reversible hydrogen electrode (RHE) and improved durability (FE loss: 13.0% vs. 55.8% after 12 h). Electrochemical analysis, in situ spectroscopy, and density functional theory (DFT) calculations reveal that mesostructure facilitates CO₂ adsorption, charge transfer, stabilizes *OCHO intermediates, and lowers the reaction energy barrier via V_O in M-SnO₂. In addition, it is shown that mesostructure promotes formation of V_O, which stabilizes the oxidation state of Sn and contributes to improved stability of the catalyst. These findings establish the synergistic roles of mesoporous structure and V_O for optimizing Sn-based CO₂RR catalysts and offer guidance for rational design of efficient CO₂RR electrocatalysts.